Wheat Comprising Male Fertility Restorer Alleles

This is a Continuation of application Ser. No. 16/760,693 filed Apr. 30, 2020, which in turn is a national stage of PCT/EP2018/079816, filed Oct. 31, 2018, which claims the benefit of: EP 18306114.2, filed Aug. 14, 2018, EP 17306501.2, filed Oct. 31, 2017, EP17306500.4, filed Oct. 31, 2017, and EP 18305027.7, filed Jan. 12, 2018. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety.

The present application contains a Sequence Listing that has been submitted electronically and is hereby incorporated by reference in its entirety. The electronic Sequence Listing is named 19177902_SequenceListing.xml, was created on Jun. 19, 2025, and is 6,085,611 bytes in size.

The invention is in the field of plant genetics and plant breeding. The invention more specifically relates to wheat plants carrying restorer of fertility genes specific toCMS cytoplasm.

Hybrid production is based on crossing two parental lines to increase heterosis and de facto, increase genetic variability to create new varieties or genotypes with higher yield and better adapted to environmental stresses. Even in a predominantly autogamous species like wheat, research studies have shown that hybrid lines exhibit improved quality and greater tolerance to environmental and biotic stresses.

In order to promote commercially viable rates of hybrid production, self-fertilization must be avoided, i.e. fertilization of the female organ by the pollen of the same plant. It is desired that the female organ of the female parent is exclusively fertilized with the pollen of the male parent. In order to obtain a reliable and efficient system for producing seeds needed for hybrid production, one generally needs three essential elements: a means to induce male sterility, a means to propagate the sterility, and a means to restore fertility. For example a fully genetically based system is composed of a male-sterile line (female parent), a fertile maintainer line (male parent allowing propagation of the male-sterile line), and a fertility restorer line (male parent for hybrid production).

Male sterility can be achieved by three different ways. Manual emasculation is the simplest one and is still used in some species where male and female flowers are separated, e.g. corn. However, it is impractical in species like wheat where flowers contain both female and male organs. Male sterility can also be induced by chemical hybridization agents (CHAs) with gametocidic effects. Currently, only a few commercial hybrid wheat cultivars are based on this technology as it can bear substantial financial risks.

Finally, male sterility can also be induced by genetic means. There are many examples of hybrid systems in corn or sorghum based on male sterility induced by genetic means showing the preponderance of this technology compared to the two mentioned previously. However, in other species which are predominantly self-pollinated like wheat, hybrid production is still a challenge (Longin et al, 2012).

The first case of male sterility in wheat was observed in 1951 (Kihara, 1951), where it was observed that sterility was caused by incompatibility between the cytoplasm ofL. and the nucleus ofvar. erythrospermum. Subsequently research on T. timopheevii cytoplasm showed that this cytoplasm is able to induce sterility in bread wheat () (Wilson and Ross, 1961, Crop Sci, 1: 191-193). Orf256 was previously identified as a gene specific to themitochondrial genome (Rathburn and Hedgcoth, 1991; Song and Hedgcoth, 1994), however, it remains to be shown that orf256 is the genetic determinant ofCMS. It was expected that such a cytoplasm could be used in a hybrid production system. However, major limitations arose from the difficulty in finding a completely dominant and stable fertility restorer gene with no negative side effects (notably on yield).

Fertility restoration of male sterile plants harboringCMS cytoplasm (T-CMS cytoplasm) has been reported and eight major restorer loci (designated as Rf1 to Rf8) have been identified and located approximate within the wheat genome. One of the most effective restorer loci is Rf3 (Ma and Sorrells, 1995; Kojima et al, 1997; Ahmed et al 2001; Geyer et al 2016). Two SNP markers allowed the location of the Rf3 locus within a 2 cM fragment on chromosome 1B (Geyer et al, 2016). The author notes that these markers are not diagnostic markers.

While it is understood that restoration to normal pollen fertility could require two or more Rf loci, it is also well known that modifier loci exist that have either minor effects with low penetrance (Zhou et al 2005, Stojalowski et al 2013) or inhibitory effects on fertility, depending on environmental conditions (Wilson, 1984). It is not yet understood which combination of genes or loci is needed to complete a full restoration of T-CMS in different genetic backgrounds and environmental conditions.

In this context, the development of technologies that enable a full restoration of pollen fertility is of major importance in wheat. It is therefore the object of this invention to propose suitable fertility restorer genes in wheat for the development of a hybrid production system useful for the seed industry.

A first object of the present disclosure relates to an isolated Rf1 nucleic acid encoding a Rf1 protein restorer of fertility ofCMS cytoplasm, wherein the corresponding amino acid sequence has at least 95% identity, preferably at least 96%, 97%, 98%, 99% or 100% identity to SEQ ID NO:361. An example of Rf1 nucleic acid comprises SEQ ID NO:3119.

The disclosure also relates to a transgenic wheat plant comprising such Rf1 nucleic acid, and, optionally, one or more nucleic acids comprising Rf3, Rf4 and/or Rf7 restorer allele(s), as transgenic element(s).

Another aspect relates to a genetically engineered wheat plant comprising such Rf1 nucleic acid, and, optionally, one or more nucleic acids comprising Rf3, Rf4 and/or Rf7 restorer allele(s), as genetically engineered element(s).

In specific embodiments, said transgenic element(s) or genetically engineered element(s) express polypeptides which restore or improve male fertility to the plant as compared to the parent plant without such transgenic element(s) or genetically engineered element(s).

Yet another aspect relates to a wheat plant restorer of fertility ofCMS cytoplasm comprising such Rf1 restorer allele, and at least two fertility restorer alleles within the restorer loci chosen amongst Rf3, Rf4 and Rf7, wherein,

The disclosure also provides methods for producing a transgenic wheat plant as described above, wherein the method comprises the steps of transforming a parent wheat plant with one or more Rf1 nucleic acids encoding protein restorer ofCMS cytoplasm, selecting a plant comprising said one or more nucleic acid(s) as transgene(s), regenerating and growing said wheat transgenic plant.

Also part of the present disclosure is a method for producing a genetically modified wheat plant as described above, wherein the method comprises the steps of genetically modifying a parent wheat plant to obtain in their genome one or more nucleotide sequence encoding Rf1 protein restorer ofCMS cytoplasm, preferably by genome-editing, selecting a plant comprising said one or more nucleotide sequences as genetically engineered elements, regenerating and growing said wheat genetically engineered plant.

The disclosure further relates to a method for producing a wheat plant by crossing, said method includes the following:

Preferably in such methods, the fertility score of the obtained wheat plant has a fertility score higher than the parent wheat plant.

The disclosure also relates to a method for producing a transgenic or genetically engineered wheat plant, wherein the fertility level of said plant is modified, comprising the step of knocking-down Rf1 restorer allele expression, wherein said Rf1 restorer allele comprises a Rf1 nucleic acid.

The disclosure also relates to the method for producing a wheat hybrid plant comprising the steps of:

The wheat hybrid plant as obtained by the above methods are also part of the present disclosure.

The present disclosure also relates to a method of identifying a wheat plant as described above, wherein said wheat plant is identified by detecting the presence of at least one restorer allele Rf1 and, optionally, one or more further restorer alleles selected from the group consisting of Rf3, Rf4 and Rf7.

Accordingly, nucleic acid probes or primers for the specific detection of the restorer allele Rf1 in a wheat plant, and, optionally, one or more of the Rf3, Rf4, and Rf7 restorer alleles, are also disclosed herein.

Another aspect of the disclosure relates to a recombinant nucleic acid comprising a Rf1 nucleic acid encoding a Rf1 protein restorer ofCMS cytoplasm, operably linked to regulatory elements and the vectors for use in transformation of a wheat plant, comprising such recombinant nucleic acids.

An aspect of the present disclosure relates to the cloning and characterization of genes encoding restorer of fertility proteins that act onCMS cytoplasm (hereafter referred as Rf genes or nucleic acids) in wheat plants and the use of the corresponding Rf nucleic acids for producing transgenic wheat plants, for modifying wheat plants by genome editing, and/or for detecting such Rf genes in wheat plants.

Whenever reference to a “plant” or “plants” is made, it is understood that also plant parts (cells, tissues or organs, seed pods, seeds, severed parts such as roots, leaves, flowers, pollen, etc.), progeny of the plants which retain the distinguishing characteristics of the parents (especially, male fertility associated with the claimed Rf nucleic acids), such as seed obtained by selfing or crossing, e.g. hybrid seeds (obtained by crossing two inbred parent plants), hybrid plants and plant parts derived therefrom are encompassed herein, unless otherwise indicated.

As used herein, the term “wheat plant” refers to species of the genusas for example,Faegi. Wheat plant also refers to species of the generaand Triticale.

As used herein, the term “restorer of fertility ofCMS cytoplasm” refers to a protein whose expression in a wheat plant comprisingCMS cytoplasm contributes to the restoration of the production of pollen in theCMS system.

As used herein, the term “allele(s)” means any of one or more alternative forms of a gene at a particular locus. In a diploid, alleles of a given gene are located at a specific location or locus on a chromosome. One allele is present on each chromosome of the pair of homologous chromosomes. The same definition is used for plants bearing a higher level of ploidy like ingender wherein, for example,is an hexaploid plant.

As used herein, the term “restorer allele ofCMS cytoplasm” refers to an allele which contributes to the restoration of the production of pollen in the CMSsystem.

The restoration of pollen fertility may be partial or complete. The pollen fertility can be evaluated by the pollen fertility tests as described in the Examples below. In particular, the fertility score of F1 wheat plants having CMS-cytoplasm (from test restorer line with CMS hybrids) may be calculated by dividing the total number of seeds threshed from a spike by the number of counted spikelets and may be compared with the fertility scores of a panel of control fertile plants, for example elite inbred lines bearing a normal wheat cytoplasm, grown in the same area and under the same agro-environmental conditions. It is preferred that such panels of lines comprise a set of at least 5 elite inbred lines wherein these lines are representative of the area where the fertility test is achieved. Besides, it is preferred that at least 10 spikes from different individual F1 plants be assessed for a given experiment.

If the fertility score is not null, then the plant has acquired partial or full restoration of fertility. For each fertility score, a statistical test is calculated to obtain a p-value. Examples of statistical tests are the Anova or mean comparison tests. A p-value below a 5% threshold will indicate that the two distributions are statistically different. Therefore, a significant decrease of the fertility score of the tested wheat plant as compared to the fertility score of the fully fertile control plant is indicative that the F1 plant has not acquired full restoration of fertility (i.e. partial restoration). A similar or higher fertility score is indicative that the F1 plant has acquired full restoration of fertility. In a preferred embodiment, the wheat plant, such as transgenic or genetically engineered wheat plant, according to the present disclosure, has acquired full restoration of fertility.

The loci of the restorer alleles ofCMS cytoplasm within Rf1, Rf3, Rf4 and Rf7 have been mapped in the present disclosure. The corresponding restorer alleles are designated Rf1, Rf3, Rf4 and Rf7 restorer alleles and have been described in the art. In particular, a wheat plant source of the Rf3 restorer allele includes the commercial following lines: Allezy, Altigo, Altamira, see table 15. A wheat plant source of the Rf4 restorer allele includes the following lines: R113 or L13.

In specific embodiments, representative alleles of Rf1, Rf3, Rf4 and Rf7 restorer alleles are provided by the seed sample chosen amongst: NCIMB 42811, NCIMB 42812, NCIMB 42813, NCIMB 42814, NCIMB 42815, NCIMB 42816, and NCIMB 42817.

As used herein, the term “centimorgan” (“cM”) is a unit of measure of recombination frequency. One cM is equal to a 1% chance that a marker at one genetic locus will be separated from a marker at a second locus due to crossing over in a single generation.

As used herein, the term “chromosomal interval” designates a contiguous linear span of genomic DNA that resides in planta on a single chromosome. The genetic elements or genes located on a single chromosomal interval are physically linked. The size of a chromosomal interval is not particularly limited. In some aspects, the genetic elements located within a single chromosomal interval are genetically linked, typically with a genetic recombination distance of, for example, less than or equal to 20 cM, or alternatively, less than or equal to 10 cM. That is, two genetic elements within a single chromosomal interval undergo recombination at a frequency of less than or equal to 20% or 10%.

The present disclosure provides nucleic acids and their recombinant forms comprising the coding sequence of either Rf1, Rf3, Rf4, Rf7 or Rf-rye restorer of fertility proteins active inCMS cytoplasm.

As used herein, a “recombinant nucleic acid” is a nucleic acid molecule, preferably a DNA molecule, comprising a combination of nucleic acid molecules that would not naturally occur together and is the result of human intervention, e.g., a DNA molecule that is comprised of a combination of at least two DNA molecules heterologous to each other, and/or a DNA molecule that is artificially synthesized and comprises a polynucleotide sequence that deviates from the polynucleotide sequence that would normally exist in nature.

Such nucleic acids encoding candidate restorer of fertility proteins ofCMS cytoplasm have been isolated as described in the Examples below. Accordingly, a first aspect of the disclosure are nucleic acids encoding a protein restorer of fertility ofhaving an amino acid sequence at least 95% identical, typically at least 96% identical, to an amino acid sequence chosen amongst any one of SEQ ID NO:1 to SEQ ID NO:1554.

Percentage of sequence identity as used herein is determined by calculating the number of matched positions in aligned amino acid sequences, dividing the number of matched positions by the total number of aligned amino acids, and multiplying by 100. A matched position refers to a position in which identical amino acids occur at the same position in aligned amino acid sequences. For example, amino acid sequences may be aligned using the CD-hit (settings -c 0.96 -n 5 -G 0 -d 0 -AS 60 -A 105 -g 1, see http://weizhongli-lab.org/cd-hit/).

The above candidate nucleic acids encoding any one of polypeptides SEQ ID NO: 1 to 1554, can further be assessed for their capacity to restore fertility of sterile wheat plant as described below.

It is therefore disclosed herein a method for assessing the capacity of a nucleic acid to restore fertility, wherein the method comprises the steps of:

In a specific embodiment, the parent wheat sterile plant is the Fielder line bearing theCMS cytoplasm.

In another specific embodiment of the above method, the Rf1, Rf3, Rf4, Rf7 and/or Rf-rye candidate nucleic acid sequence is selected from those encoding an amino acid sequence having at least 95% identity, or at least 96% identity, for example 100% identity, to any one of SEQ ID NO1 to SEQ ID NO1554.

Typically, the Rf1, Rf3, Rf4, Rf7 and/or Rf-rye candidate nucleic acids are selected among the following nucleic acids of SEQ ID NO:1555 to SEQ ID NO:3107 and 3133.

In a further specific embodiment, where appropriate, the nucleic acid sequence may be optimized for increased expression in the transformed plant. There are a number of optimizations that can be performed at the DNA level, without changing the protein sequence, by conservative codon exchanges which replace one codon by another codon encoding the same amino acid. Besides, the nucleic acid sequence can be modified for cloning purpose. Like for optimization, such modification is achieved without changing the protein sequence.

In specific embodiment, the nucleic acid of the present disclosure is a Rf1 nucleic acid.

As used herein, the term “Rf1 nucleic acid” refers to a nucleic acid comprising a gene encoding a Rf1 protein restorer of fertility ofCMS cytoplasm, wherein the corresponding amino acid sequence has at least 95% identity, preferably, 96%, 97%, 98%, 99% or 100% identity to an amino acid sequence selected from the group consisting of SEQ ID NOs1-2, SEQ ID NOs288-290, SEQ ID NOs293-296, SEQ ID NOs343-346, SEQ ID NOs349-354, SEQ ID NOs359, 361 and 362, SEQ ID NOs 396 and 397, SEQ ID NOs428-430, SEQ ID NO517 and 519, SEQ ID NOs752-754, SEQ ID NOs1092, 1093 and 1095, typically, SEQ ID NOs359, 361 and 362 and SEQ ID NO428-430. In a particularly preferred embodiment, the Rf1 nucleic acid encodes an amino acid sequence having at least 95% identity, preferably, 96%, 97%, 98%, 99% or 100% identity to SEQ ID NO:361. Examples of corresponding specific Rf1 nucleic acids are referred to in Table 7.